diff --git a/build.zig b/build.zig
index ec893c547b..1a0972c5cd 100644
--- a/build.zig
+++ b/build.zig
@@ -733,7 +733,7 @@ pub fn build(b: *std.Build) !void {
     zig0_airgen_options.addOption(bool, "llvm_has_arc", false);
     zig0_airgen_options.addOption(bool, "llvm_has_xtensa", false);
     zig0_airgen_options.addOption(bool, "debug_gpa", debug_gpa);
-    zig0_airgen_options.addOption(DevEnv, "dev", dev_mode);
+    zig0_airgen_options.addOption(DevEnv, "dev", .full);
     zig0_airgen_options.addOption(ValueInterpretMode, "value_interpret_mode", value_interpret_mode);
     zig0_airgen_options.addOption([:0]const u8, "version", try b.allocator.dupeZ(u8, "0.15.2-zig0-dev"));
     zig0_airgen_options.addOption(std.SemanticVersion, "semver", try std.SemanticVersion.parse("0.15.2-zig0-dev"));
@@ -746,7 +746,9 @@ pub fn build(b: *std.Build) !void {
     zig0_airgen_options.addOption(u32, "tracy_callstack_depth", tracy_callstack_depth);
     zig0_airgen_options.addOption(bool, "value_tracing", value_tracing);
 
-    const air_gen_result = addAirGen(b, zig0_airgen_options, optimize);
+    // ReleaseFast, because we trust compiler will emit the correct AIR
+    // under all modes.
+    const air_gen_result = addAirGen(b, zig0_airgen_options, .ReleaseFast);
 
     const prepare_zig0 = b.step("prepare-zig0", "Generate pre-computed AIR files for zig0 tests");
     prepare_zig0.dependOn(air_gen_result.step);